Batson went fist to Thor's hammer. Thor was able to sling a heavy piece of funfair machinery on him and Marvel decided to change into Billy.

Seeing this, Thor sacrificed his hammer in a desperate bid to prevent the lightning. It's an interesting take from the writers, where they obviously didn't want to show Thor ko'ing him.

In a sense, it shows Adam would be a greater foe. Teth Adam is the same size and Adam doesn't hold back. No tactical sense for him to change and Adam's temperament makes him a different kettle of fish. It's often remarked that his ferociousness can make him a match for several top tier heroes when combined with his speed and strength.

It's likely a fist fight wouldn't go Thor's way, especially now Thor has no hammer and only one arm. He is truly the one armed bandit.